Process for removing copper oxide from processing equipment



United States Patent US. Cl. 134-2 3 Claims ABSTRACT OF THE DISCLOSURE Copper-containing residues of polyamide or degradation products thereof are removed from processing equipment, such as steel melt-spinning equipment, by treating the equipment with a hot aqueous solution containing 20% by weight of an ammonium salt of an inorganic acid. The treatment may be preceded by exposing the equipment to a mixture of steam and air at a temperature of 300 C.- 600" C.

This invention relates to a process for removing copper compounds from processing equipment.

In order to enhance the stability toheat and/ or light and/or oxygen of high molecular weight linear fibrefor-ming polyamides e.g. polyhexamethylene adipamide, there are commonly added thereto small quantities of copper or copper compounds frequently accompanied by a halide. Although very little of the copper is normally present in the polyamide, copper-containing deposits gradually accumulate on processing equipment such as melt-spinning apparatus through which the molten polyamide passes during its extrusion in the form of filaments. The melt-spinning apparatus commonly comprises a grid, melt-pool, spinneret and pumps all of which are usually made of steel.

A well known process of cleaning the processing equipment which has become fouled with residues of polyamide or degradation products thereof, comprises exposing the equipment to an atmosphere of steam and air at 300- 600 C. This treatment however fails to remove the copper-containing deposits referred to above. When copperfree colourless polyamide is melt-spun through equipment bearing copper-containing deposits the issuing polymer bears copper and is unsatisfactory, often exhibiting a pink or purple hue. It is then necessary to spin much polyamide and discard it as waste before the copper is eliminated and the desired colourless polyamide obtained. This procedure is time consuming and wasteful. Means of removing the copper-containing deposits have accordingly been sought.

The copper-containing deposits appear to consist substantially of copper oxide. A suitable reagent for their removal should be cheap and not sensibly corrode the steel equipment. 'It is thus desirable that the reagent be capable of cleaning a large quantity of equipment without risk of the copper becoming re-deposited owing to the concentration thereof accumulating in the solution.

It has now been found that the copper-deposits can be efficiently removed by treatment with a reagent consisting of a hot aqueous solution containing an ammonium salt of an inorganic acid, said ammonium salt being defined as one which produces an aqueous solution having a pH value in the range from 6 to 10, followed by washing with water.

Examples of suitable ammonium salts are:

diammonium hydrogen phosphate ammonium carbonate triammonium phosphate.

Advantageously there is also added to the reagent a rust inhibitor, for example, a small percentage e.g. /2 or 1% by weight, of sodium nitrite.

Accordingly, the invention consists of a process for removing copper-containing deposits from equipment comprising treating the latter with a hot aqueous solution containing an ammonium salt of an inorganic acid, as hereinbefore defined, and washing with water.

The temperature of the solution is suitably at least C, andthe time of treatment may be, for instance, one hour. The concentration of the ammonium salt of the inorganic acid is preferably from 10 to 20% weight by weight.

Conveniently, in the case of equipment employed for melt-spinning polyamides, the present treatment with an ammonium salt is preceded by a cleaning process comprising exposing the equipment to a mixture of steam and air at 300-600 C.

The following examples are intended to illustrate not limit the invention; the percentages and parts expressed therein are calculated on a weight basis.

EXAMPLE 1 Polyhexamethylene adipamide containing 35 parts per million of copper added as copper acetate and 700 parts per million of iodine added as hexamethylene diammonium iodide, is melt-spun through a grid melter similar to that described in British specification 533,307 for a period of 3 weeks at the rate of 20* lbs. per hour. The grid melter is thereupon cleaned by treatment with a mixture of steam and air at 500 C. The grid melter is then heated for 1 hour in a 10% aqueous solution of diammonium hydrogen phosphate at C. After this treat-ment the grid melter is thoroughly washed with water and dried.

Copper-free polyhexamethylene adipamide is melt-spun through the cleaned melter at 20 lbs. per hour. At the end of 15 minutes the extruded polymer when analysed is found to contain only 7 parts per million of copper; moreover the extruded filaments are colourless.

When the treatment with the diammonium phosphate according to the present invention is omitted, the copperfree polyamide after extrusion is found to contain (after 15 minutes extrusion) parts per million of copper; the extruded filaments have a pink hue.

EXAMPLE 2 Example 1 is repeated except that instead of diammonium hydrogen phosphate there is employed triammonium phosphate, and 0.5% sodium nitrite is dissolved in the aqueous solution thereof. Similar results are obtained.

EXAMPLE 3 Polyhexamethylene adipamide containing 5 parts per million copper as copper acetate and 310 parts per million iodine added as hexamethylene diammonium iodide, is melt-spun through a grid melter similar to that described in British specification for a period of 3 weeks at the rate of 15 lbs. per hour.

The grid melter is cleaned by treatment with a mixture of steam and air at 500 C. The melter is then immersed in a 20% aqueous solution of diammonium hydrogen phosphate at 80 C. for 1 hour; the melter is afterwards rinsed with water and dried.

Copper-free polyhexamethylene adipamide is melt-spun through the cleaned melter at 15 lbs.'per hour. The extruded polymer is analysed for copper after various periods of spinning, the results being tabulated below.

Parts per million Time in minutes: of copper 7 The extruded filaments are colourless.

What I claim is:

1. The one step process for removing copper-containing deposits from equipment consisting of treating the latter with a hot solution consisting essentially of water and from 10% to 20% by Weight of an ammonium salt of an inorganic acid, said salt producing an aqueous solution having a pH in the range from 6 to 10, and washing with water.

2. Process for removing copper-containing deposits from equipment comprising treating the latter with a hot aqueous solution at a temperature of over 80 C. containing from 10% to 20% weight by Weight of diammo- References Cited UNITED STATES PATENTS 1,484,690 2/ 1924 Walker et a1.

1,765,331 6/1930 Gravell 13441 XR 2,567,835 9/1951 Alquist et al 134-22 XR 3,000,767 9/1961 Elliott 13422 XR 3,231,503 1/1966 Laue 25279.l

JOSEPH SCOVRONEK, Primary Examiner D. G. M ILLMAN, Assistant Examiner US. Cl. X.R. 

